The present invention relates to a substrate for an electronic power circuit, and more particularly to a substrate that needs to withstand a large potential difference between the various conductive tracks placed on one face of the substrate and the opposite face of the substrate, while nevertheless providing good heat exchange. The substrate of the invention is for supporting power semiconductors, and in particular isolated gate bipolar transistors (IGBT) as used in power distribution circuits in the railway field and in the power transport field in which voltages are particularly high.
In the prior art it is known to have substrates for electronic power circuits that comprise an electrically insulating wafer of alumina with its bottom and top surfaces being covered in respective copper sheets having a thickness of about 300 micrometers (xcexcm), the sheets being applied by using the direct bonding copper (DBC) method. To improve cooling, a radiator is placed in contact with the bottom copper sheet so as to dump the heat given off by the power components.
It is also known to improve the performance of such a substrate, and in particular to reduce its thermal resistance, by replacing the electrically insulating wafer of alumina with an insulating material that possesses better thermal conductivity, such as aluminum nitride AlN. Nevertheless, such a substrate presents the drawback of having bonding layers formed by the DBC method at the interface between the AlN wafer and the copper metallization, said layers constituting a thermal barrier that greatly reduces the heat transmission capacity of the substrate. Improving the performance of such a substrate thus requires the properties of the insulating material to be improved and the quality of the interface between the copper and the insulating material to be improved, and that cannot be achieved with the DBC method.
The object of the present invention is thus to propose a novel type of substrate for receiving electronic power components and possessing improved performance, in particular reduced thermal resistance, and which is simple and of low cost to make.
To this end, the invention provides an electronic power circuit substrate including a wafer of electrically insulating material, wherein said wafer presents a face supporting one or more conductive tracks directly connected to one or more electronic power components, said conductive tracks being obtained by fine metallization to a thickness that is less than 150 xcexcm.
In particular embodiments, the substrate for an electronic power circuit can include one or more of the following characteristics taken singly or in any technically feasible combination:
the conductive tracks are made of copper and are obtained by electrolytic growth;
the thickness of the copper conductive tracks lies in the range 100 xcexcm to 150 xcexcm;
the electronic power components are IGBT components;
the wafer is made of aluminum nitride;
the bottom face of the wafer has channel-forming stripes in which a cooling fluid flows; and
the wafer has a single metallized face.
The invention also provides an electronic power module including at least one electronic power component mounted on a substrate in accordance with the above-described characteristics.